1. Field of the Invention
The present invention is related to air pollution control equipments and particularly to a precipitator of tube bundle heat exchanger of constant temperature gradient for thermophoretic deposition of aerosol particles.
2. Description of the Related Art
A conventional pipe bundle heat exchanger for thermophoretic deposition of aerosol particles, which was disclosed in Aerosol Science and Technology by A. Messerer et al., comprises a stainless steel channel and a plurality of miniature pipe bundles. The miniature pipe bundles arranged in the channel are cooled by the inflowing cooling air. When the hot exhaust gas for the treatment is flowing between the miniature pipes and the channel, the temperature gradient between the outer tubes and the walls of the heat exchanger causes aerosol particles suspended in the exhaust gas to deposit on the walls of the cooler miniature pipes due to thermophoresis, and therefore the exhaust gas is purified.
However, thermal gradient is high near the entry of the heat exchanger and decreases exponentially with increasing downstream distance of the flow. This limits the effective deposition region near the entrance of the precipitator and thermophoresis force strongly decreases along the flow direction. Thus, heavy particle deposition near the entrance occurs to cause undesired pressure drop. The effects of entrance clogging lower overall particle removal efficiency.